1. Field of the Invention
The present invention relates to a method and apparatus for trimming a thermoformed film. More specifically, the invention relates to a method and apparatus for trimming the film in conjunction with the thermoforming operation.
2. Description of the Related Arts
It is known to manufacture molded articles by injection molding a backing to a decorative sheet. The method is described in U.S. Pat. No. 3,668,034 (""034). The ""034 patent teaches placing a decorative laminate within a mold and then injection molding a polymeric material behind the laminate. The resin inlet is juxtaposed to the laminate backing. The polymeric material heats, softens and finally fuses to the backing on the laminate.
This reference does not disclose forming the film, but the illustrations are two relatively simple two-dimensional films. These films are easily positioned within a tool and molded into an article. Larger articles with three-dimensional surfaces are much more difficult to properly align within a tool. They must be precisely trimmed to the desired dimension. Because these articles are three-dimensional, it is difficult to precisely trim the article after it is molded. The films are easily trimmed while they are flat, but it is desirable to leave the films untrimmed to have excess material. The excess material is useful to retain the film during the thermoforming operation to enable the film to stretch over the mandrel. Films are normally trimmed after they have been formed.
Heretofore, in-mold film laminates have been manufactured using movable molds and stationary cores as illustrated in U.S. Pat. No. 5,514,427 (""427). The ""427 patent teaches a mold press having a stationary core. The resin inlet is placed within the core and injects molten plastic material behind the film. The ""427 patent does not teach how the finished molded article is removed from the press. U.S. Pat. No. 5,599,608 similarly teaches a movable core having a resin inlet injecting plastic behind the film.
U.S. Pat. No. 5,599,608 teaches a method of thermoforming a film on a mandrel and then trimming the film after it is removed from the mandrel. After the film is molded, it is trimmed. The U.S. Pat. No. 5,599,608 does not teach trimming the film while still on the forming mandrel. Removing the film from the forming mandrel requires properly locating the precise location on the film for trimming. Because the film is flexible and formed in a three-dimensional shape, locating these areas precisely is difficult and time consuming. It also requires an additional manufacturing step. It is desirable to trim the film while it is still on the forming mandrel because the precise location on the film is easily and repeatably identified. It is also desirable to combine the forming and trimming operation to take advantage of the dwell time on the mandrel while the film is cooling.
These deficiencies and problems are overcome by the present invention.
The present invention relates to a method of trimming a thermoformed film comprising the following steps. A thermoplastic flexible film is placed within a frame. The film and frame are heated sufficiently to make the film pliable. The film and frame are moved to a position adjacent a forming mandrel. The forming mandrel is moved against the film and causes the film to conform to the shape of the mandrel. After the film has fully conformed to the shape of the mandrel, the mandrel and film are moved to a trimming station. Knives on the trimming station contact and cut the film. It is also desirable for the knives to be mounted on actuators to move them from extended to retracted positions. The plurality of knives are used to trim around a three-dimensional article.
The present invention also provides an apparatus to trim an article. The apparatus includes a frame receiving a flexible film. The frame clamps the perimeter of the film. A heater heats the film sufficient to make the film pliable. The film and frame are moved adjacent a forming mandrel. The mandrel is movable between first, second and third positions. The film is placed adjacent the mandrel while the mandrel is in the first position. The mandrel is moved to a second position and contacts the film. The frame restrains the perimeter of the film and causes the film to take the shape of the mandrel. While the film is still pliable, the mandrel is moved to the third position. The film and mandrel enter a trimming station that trims the film perimeter while the film is on the mandrel.
It is desirable that the mandrel be used to locate the precise areas of the film that are cut. The trimming station includes movable knives that extend and retract to trim the film against the mandrel. In this way, the film is easily and repeatably trimmed to the desired dimension. The film finishes cooling on the mandrel and is then later removed.
The present invention enables the use of traditional molding mandrels. Because the film is retained on the mandrel, it is precisely trimmed in the same location. The invention greatly facilitates the manufacture of large complex articles that require trimming a three-dimensional film.
These and other desired objects of the present invention will become more apparent in the course of the following detailed description and appended claims. The invention may best be understood with reference to the accompanying drawings wherein illustrative embodiments are shown.